RF signal divider/combiners are used in the electronics industry to either divide or combine RF signals. When operating as a signal divider, one input signal is divided into a plurality of output signals, each retaining the same signal characteristics but having a lower power level than the input signal. As a power combiner, a plurality of input signals is combined into a single output signal, with the output signal having the signal characteristics of the sum of the plurality of input signals. Thus, a divider/combiner can operate as either a signal divider or a signal combiner, depending on the direction of the signals.
The electronics industry typically uses "Wilkinson" divider/combiners. In a Wilkinson divider, an input signal is split through the use-of several one-quarter wavelength (1/4.lambda.) impedance matching transformers and output impedance lines. The same device, operating in reverse, serves as a signal combiner. A Wilkinson divider/combiner is illustrated in FIG. 1.
Referring to FIG. 1, a Wilkinson divider/combiner is indicated generally by the numeral 10. As a signal divider, the circuit comprises a single input port 11 (or output port, when operating as a signal combiner) with four corresponding output ports 12 (or input ports when acting as a combiner) and four resistive elements 13, as well as their associated interconnections. Although four output (or input) ports are shown, any number, n, of output (or input) ports may be used. The Wilkinson circuit thus operates to either divide one input into n outputs or combine n inputs into one output.
The Wilkinson divider/combiner, however, has limited power handling capability. The "resistive star" created by the resistive elements 13 make the Wilkinson circuit difficult to realize in practice. In microstrip embodiments, for example, many Wilkinson divider/combiners are subject to signal crossover, resulting in ineffective circuit isolation. In addition, the resistors commonly used for the resistive elements 13 generally limit the power-handling capability of the Wilkinson device to less than 100 watts.
Other divider/combiners have been developed to replace Wilkinson divider/combiners in high power situations. The Gysel divider/combiner is one such circuit, shown in FIG. 2. This divider/combiner circuit is indicated generally by the numeral 20. In the Gysel divider/combiner, operating as a signal divider, an input signal is applied to an input port 21. A plurality of 1/4.lambda. transmission lines 24 divide the input signal among a plurality of output ports 22. Other transmission lines 25 connect each of the output ports to shunt-connected resistors 27. Additional transmission lines 26 connect each of the resistors 27.
The Gysel-type divider/combiner offers advantages in implementation over the Wilkinson-type divider combiner because it avoids the use of a resistive star. In addition, the transmission lines and shunt-connected resistors of the Gysel-type divider/combiner allow it to achieve much higher power-handling abilities. Unfortunately, the increased power-handling abilities come at the expense of increased size. Because of the long transmission lines, the Gysel-type divider/combiner is relatively large.
Other power divider and power combiners are exemplified by U.S. Pat. No. 4,721,929 to Schnetzer, U.S. Pat. No. 4,595,891 to Cronauer, U.S. Pat. No. 5,021,755 to Gustafson, U.S. Pat. No. 4,647,879 to Vaddiparty, and U.S. Pat. No. 4,835,496 to Schellenberg et al. These patents each teach circuitry that is operative to combine or divide power. However, for the above reasons with respect to the Wilkinson and Gysel circuits, these combiner/dividers do not provide optimal performance in a high power, low space enviroment.
Accordingly, it is an object of the present invention to develop a microwave divider/combiner that is relatively small but has high power-handling abilities.